Lyotropic Liquid Crystalline Solutions Research Articles

Nanotubes of a Different Kind: Stoichiometry and Geometry of the Orange II/γ-Cyclodextrin Complex in Water.

Orange II (O-II), a water-soluble ionic azo dye, aggregates and eventually forms needle-like crystals at concentrations greater than 0.15 M. However, when equimolar amounts of γ-cyclodextrin (γ-CD) are added to solutions containing O-II at 0.025 M or higher, the solution's appearance rapidly changes presenting a viscous, birefringent liquid, a lyotropic liquid crystalline solution. Birefringence is absent when viewing aqueous solutions of only O-II or γ-CD at concentrations greater than 0.03 M. Using ultraviolet-visible (UV-vis) and fluorescence spectroscopy, coupled with conductivity measurements, we postulate a structure for the basic "building block" of the self-assembly that eventually gives rise to a rodlike superstructure, leading to the formation of a lyotropic liquid crystalline phase.

Analysis of spinnable mesophase pitch in terms of lyotropic liquid crystalline solution

Analysis of spinnable mesophase pitch in terms of lyotropic liquid crystalline solution

Treating anisotropic artefacts in circular dichroism spectroscopy enables investigation of lyotropic liquid crystalline polyaspartate solutions.

Circular dichroism (CD) spectroscopy is commonly used for investigation of the secondary structure of biomolecular compounds as well as polymers in isotropic solution. In anisotropic solution, the usage of the apparent CD is prone to misinterpretations due to artefacts from contributions of e.g. linear dichroism (LD). Herein, a method for the complete cancelation of anisotropic artefacts in the apparent CD is developed and its validity proven. The approach is further used for investigation of the conformation and the lyotropic liquid crystalline (LLC) structure of a copolyaspartate. For this system, a temperature-dependent change of the polymer's helical conformation (helix reversal) is known. Furthermore, a rotation of the aligned polymer helices inside a magnetic field (helix realignment) is independently present, occurring at a lower temperature compared to the helix reversal. In the current study, the helix reversal is confirmed and found to be accompanied by a change of the LLC structure. A cholesteric structure is detected and revealed to change its sense (cholesteric reversal) at the temperature at which the helix realigns in the magnetic field. The determination of the cholesteric sense is enabled by measuring the induced CD of an achiral dye, dissolved in the anisotropic polymer solution. Investigation of the anisotropic polymer solution is, thus, only made possible by cancellation of the aforementioned anisotropic artefacts. This allows the observation of changes of the liquid crystal structure from right-handed cholesteric, through left-handed cholesteric, to nematic with increasing temperature.

Playing the blues, the greens and the reds with cellulose-based structural colours.

Structural vivid colours can arise from the interference of light reflected from structures exhibiting periodicity on scales in the range of visible wavelengths. This effect is observed with light reflected from cell-walls of some plants and exoskeletons of certain insects. Sometimes the colour sequence observed for these structures consists of nearly circular concentric rings that vary in colour from Red, Orange, Yellow, Green, Cyan to Blue, from the periphery to the centre, similarly to the colour scheme sequence observed for the rainbow (ROYGB). The sequence of colours has been found for solid films obtained from droplets of aqueous cellulose nanocrystals (CNCs) suspensions and attributed to a "coffee ring" effect. In this work, coloured lyotropic solutions and solid films obtained from a cellulose derivative in the presence of trifluoroacetic acid (TFA), which acts as a "reactive solvent", are revisited. The systems were investigated with spectroscopy, using circularly and linearly polarised light, coupled with a polarised optical microscope (POM) and scanning electron microscopy (SEM). The lyotropic cholesteric liquid crystalline solutions were confined in capillaries to simplify 1D molecular diffusion along the capillary where an unexpected sequence of the structural colours was observed. The development and reappearance of the sequence of vivid colours seem consistent with the reaction-diffusion of the "reactive solvent" in the presence of the cellulosic chains. The strong TFA acts as an auto-catalyst for the chemical reaction between TFA and the hydroxyl groups, existing along the cellulosic chain, and diffuses to the top and bottom along the capillaries, carrying dissolved cellulosic chains. Uncovering the precise mechanism of colour sequence and evolution over time in cellulosic lyotropic solutions has important implications for future optical/sensors applications and for the understanding of the development of cellulose-based structures in nature.

Study of first normal stress difference of poly(p-phenylene terephthalamide) in sulfuric acid

The first normal stress difference (N1) of lyotropic liquid crystalline solutions of poly(p-phenylene terephthalamide) (PPTA) in sulfuric acid was studied by rheometric measurements. For the first time, a negative value range of N1 was observed for the solutions in a high shear rate range. N1 showed a non-monotonic dependence on the shear rate when the PPTA/sulfuric-acid solution was in the nematic phase. The minimum value of the first normal stress difference (N1min) and the shear rate to achieve N1min (γ˙min) were observed to be closely correlated with temperature, concentration and molecular weight. Compared with some well-studied lyotropic LCP systems, the rheological behavior of PPTA/sulfuric-acid was more sensitively dependent on the concentration. Above observations indicate that the frustration of tumbling of average polymer orientation occurs in the high shear rate range and the influences of the factors are not exactly the same as those well-studied lyotropic LC polymer systems.

Anomalous rheological behavior of long glass fiber reinforced polypropylene

Dynamic rheological properties of PP-based long glass fiber-reinforced thermoplastics (LFT) were investigated. Weight fractions of the glass fibers investigated in the present study ranged from 0.15 to 0.5, which are higher than those of previous studies. We observed very abnormal rheological behavior. Complex viscosity (η*) of the LFT increased with the glass fiber content up to 40 wt. %. However, the η* with a weight fraction of 0.5 is observed to be lower than that of LFT with a weight fraction of 0.4 in spite of higher glass fiber content. From various experiments, we found that this abnormal behavior is analogous to the rheological behavior of a lyotropic liquid crystalline polymer solution and concluded that the abnormal rheological behavior for the LFT is attributed to the formation of a liquid crystal- like structure at high concentrations of long glass fibers.

Anisotropic Swelling Behavior Induced by Helix-Coil Transition in Liquid Crystalline Polypeptide Gels.

Uniaxially oriented liquid crystalline poly(γ-benzyl l-glutamate) (PBLG) gel was prepared by cross-linking the lyotropic liquid crystalline PBLG solution in magnetic field, and PBLG was converted to poly[N5-(2-hydroxyethyl) l-glutamine] (PHEG) by side-chain aminolysis reaction. The prepared PHEG gel retained the liquid crystallinity after the conversion from PBLG to PHEG when immersed in α-helix-forming solvent such as ethylene glycol. By the addition of water into the immersion solvent, conformational transition of PHEG from α-helix to random coil was occurred, and the optical anisotropy of the gel was disappeared. With this helix-to-coil transition of PHEG, the gel was swollen in the direction perpendicular to the orientational axis of PHEG, and was shrunk in the parallel direction. As the result, the gel in cylindrical shape in ethylene glycol, in which α-helical PHEG is oriented along the cylindrical axis, changed to more isotropic shape in water. This anisotropic shape change of the gel was described by the conformational transition of the cross-linked PHEG from the anisotropic rodlike α-helix to the isotropic random coil.

Intercalated polyaniline nanosheets prepared from lyotropic liquid crystalline solutions and their capacitive performance

Intercalated polyaniline (PANI) nanosheets, supported by sodium dodecyl sulfate (SDS), have been prepared in one step from discotic nematic lyotropic liquid crystal (LLC) solutions. The inter-lamellar distance was observed to be dependent strongly on the stirring situation during the polymerization: an average distance of 3.4 nm is favorable for samples with and without stirring during the preparation, while a shorter one of 1.4 nm is preferable when the system was stirred only during the period of the addition of ammonium persulfate (APS). Interestingly, all UV–vis, XPS, TGA and elemental analysis experiments demonstrate clearly that the PANIs prepared in this way were in partially doped states, although all these reactions were carried out at non-acidic conditions. Such phenomenon can be attributed to the doping process induced by dodecyl sulfuric acid, which was produced in situ during the polymerization. Furthermore, all our PANIs exhibit high specific capacitance in compared with other chemically prepared systems. In particularly, superior capacitance retention propriety (as high as 86.7% in a current density of 0.4–4.0 A g −1) can be available for PANI prepared with stirring all the time, indicating its great potential to provide high power density. In short, our experiments indicate that the intercalated nanosheet structure at molecular scale is of great benefit in improving the supercapacitive performance of the corresponding electrode material in supercapacitors.

Preparation of TiO 2/polyaniline nanocomposite from a lyotropic liquid crystalline solution

Nanocomposites with two-dimensional (2D) lamellar polyaniline (PANI) as the matrix and TiO 2 as the disperse phase have been prepared in a single step from discotic nematic lyotropic liquid crystal (LLC) solutions as composed by sodium dodecyl sulfate (SDS). Our experiment suggests that, upon loading inorganic species, the crystallinity along the perpendicular direction of PANI chains is improved; the overall morphology is nearly unchanged except the distribution of the interlamellar distances becomes much wider. Finally the thermogravimetric measurement suggests that approximately as high as 36.3% (weight%) of TiO 2 can be introduced into the polymer matrix.

Coarse-Grained Molecular Dynamic Simulations for Lyotropic Liquid-Crystalline Solutions of Semiflexible Rod-Like Molecules

Coarse-grained molecular dynamic simulations are performed for lyotropic liquid-crystalline (LC) solutions of semiflexible rod-like molecules, which are realized by harmonic-stretching potential and angle-bending potential. The phase behavior and molecular dynamic information are investigated. When the concentration of rod-like molecules increases, the solution transits from isotropic to binary phase and then to anisotropic phase. The influences of chain length, temperature, solvent solubility, and chain rigidity are studied. The simulation for the phase behavior successfully reproduces the predictions of Flory lattice theory on the rod-like molecule solution. The decrement of the chain rigidity increases the concentration of phase transition, and the apparent persistence length is increases by molecular alignments with LC formations at higher concentrations.

Mesoporous Silver Films from Dilute Mixed‐Surfactant Solutions by Using Dip‐Coating

Mesoporous silver films (see figure) are synthesized by using a dip-coating method, employing dilute mixed-surfactant solutions, which allows the creation of films over a large area of substrate and uses a smaller amount of surfactant than previous syntheses using lyotropic liquid-crystalline solutions. Ordered 2D hexagonal mesoporous silver films form under conditions of moderate humidity by using photocatalytic reduction.

Tunable topographical cellulose matrices for electro-optical liquid crystal cells

AbstractIn this work we have used acetoxypropylcellulose (APC) to produce free standing solid films (∼60 μm) that were used for assembling electro-optical devices. Thin films were obtained from concentrated lyotropic solutions of cellulose derivatives. Induced by the cast and shearing preparation conditions wrinkles and band textures can be observed in their free-surface plane. In order to eliminate and control these textures we used a process similar to that introducted in literature [1] which consists of storing the films in the same solvent-vapour atmosphere as the solution system. Lyotropic APC liquid crystalline solutions in dymethylacetamide (DMA) with crosslinker were prepared, thin films were obtained by using a shear/casting technique and stored in the solvent-vapour atmosphere until a planar structure was achieved. The dried crosslinked films were analyzed by optical polarised microscopy (POM) and scanning electron microscopy (SEM). The films with different topographies were used to produce optical cells composed by the cellulose derivative film covered on both free surfaces by a layer of the nematic liquid crystal E7 and placed between two transparent conducting substrates. The electro-optical properties of these cells were obtained.

Synthesis, Structure, and Properties of PBO/SWNT Composites&

Poly(p-phenylene benzobisoxazole) (PBO) has been synthesized in the presence of single-wall carbon nanotubes (SWNTs) in poly(phosphoric acid) (PPA) using typical PBO polymerization conditions. PBO and PBO/SWNT lyotropic liquid crystalline solutions in PPA have been spun into fibers using dry-jet wet spinning. The tensile strength of the PBO/SWNT fiber containing 10 wt % SWNTs is about 50% higher than that of the control PBO fibers containing no SWNTs. The structure and morphology of these fibers have been studied.

Blending as a method of tuning reflection wavelength and helical twisting sense in films and composites of liquid crystalline cellulose derivatives

Ethyl cellulose (EC) with a degree of substitution of 2.41 and a fully acetylated sample (AEC) of this material, form lyotropic liquid crystalline solutions in chloroform and acrylic acid. Above 35 wt% polymer, the solutions exhibit chiral nematic phases that reflect light selectively at a specific wavelength λ 0. For EC solutions the helical twist sense of the chiral nematic phase is left handed, whereas the AEC solutions are right handed. The λ 0 and handedness of the system can be tuned to a given set of values by preparing solutions of EC and AEC in different blend ratios. These can be converted to films or composites, that retain the chiral nematic structure and the corresponding chiro-optical properties, by either casting from chloroform or photopolymerising the (EC+AEC)/acrylic acid solutions to form blend composites of EC/AEC in poly(acrylic acid). The most effective way to control the chiro-optical properties of the dry films was to use the photopolymerisation technique to form composite films of the blends. Such films can be used either as coatings to reflect visible light of a particular colour, or act as a protective layer to reduce UV degradation.

Flow-induced structure in a thermotropic liquid crystalline polymer as studied by SANS

Small-angle neutron scattering is utilized to determine the flow induced alignment of a model thermotropic liquid crystalline polymer (LCP) as a function of shear rate and temperature. The results demonstrate that the flow-induced structures in thermotropic liquid crystalline polymers have similarities and differences to those in lyotropic liquid crystalline polymer solutions. The shear rate dependence of the alignment shows that the flow-induced alignment correlates very well to the viscosity behavior of the LCP in the shear thinning regime, while temperature variation results in a change in the extent of alignment within the nematic phase. Relaxation results also demonstrate that the flow-induced alignment remains essentially unchanged for up to an hour after the shear field has been removed. Last, there exists a regime at low shear rate and low temperature where alignment of the LCP molecule perpendicular to the applied shear flow is stable. These results provide important experimental evidence of the molecular level changes that occur in a thermotropic liquid crystalline polymer during flow, which can be utilized to develop theoretical models and more efficiently process thermotropic polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3017–3023, 1998

Small-angle neutron scattering from a hexagonal phase under shear

The shear orientation of a micellar hexagonal liquid crystalline phase was investigated by small-angle neutron scattering. The hexagonal phase in the quiescent state showed a symmetrical scattering pattern typical of a polydomain structure. Enhanced scattering along the flow direction was observed during shear and the anisotropy of scattering intensity became stronger with increasing shear rate. The anisotropic scattering pattern corresponds to an orientation perpendicular to the flow direction and can be interpreted as a log-rolling state. The oriented sample did not relax after cessation of shear. The results from small-angle neutron scattering confirm data obtained previously from rheo-small angle light scattering measurements and are discussed in comparison to shear alignment of lyotropic liquid crystalline polymer solutions.

Crosslinked hydroxypropyl cellulose films retaining cholesteric liquid crystalline order. I. Effects of cast conditions and heat treatment on the textures and order of films

AbstractTo eliminate the shear‐induced band texture and wrinkled texture observed on the free surface of cellulosic solid cast films retaining cholesteric liquid crystalline order, we proposed a storing process of the cast solutions: the solution is stored in the same solvent vapor atmosphere as the solution. The effect of cast conditions (the storing time) on those textures and the cholesteric liquid crystalline order was determined using the lyotropic liquid crystalline solution of hydroxypropyl cellulose in methanol with crosslinker. Furthermore, the effect of heat treatment on the liquid crystalline order in the cast films was determined. The resultant crosslinked films were observed with a polarized microscope and a scanning electron microscope, and were investigated with circular dichroism. Our findings showed that the proposed storing process is needed before starting the cast process. During the process the textures vanished, due to the relaxation of the residual stress in the solution, the cholesteric liquid crystalline order became stable, and the cholesteric pitch decreased with increasing storing time. The heat treatment also affected the liquid crystalline order of the films; the peak in the circular dichroism spectrum sharpened and shifted with heat treatment, and the shift in peak seemed to depend on the crosslinker concentration. Furthermore, the crosslinking proceeded with heat treatment. © 1995 John Wiley & Sons, Inc.

Microstructural Characterization of Crosslinkable p-Phenylene Terephthalamide-Terephthalic Acid Derivative Copolymer Fibers

We are studying the microstructure of PPTA-co-XTA copolymer fibers. XTA is a variant of terephalic acid (TA) with a benzocyclobutene (BCB) cross-linking moiety which becomes reactive above the synthesis and processing temperatures but below the degradation temperature. The fibers were dry-jet wet spun from lyotropic liquid crystalline solutions and heat-treated at various temperatures to induce structural reorganization and cross-linking. The microstructure was examined by wide-angle X-ray diffraction and molecular modeling. The copolymers retain the ability to crystallic and form well-oriented fibers

Uniaxial Extension of a Lyotropic Liquid Crystalline Polymer Solution

Uniaxial extensional stress growth of a lyotropic liquid crystalline polymer solution consisting of 40 wt% (hydroxypropyl)cellulose in glacial acetic acid was measured using a filament stretching technique. The Doi molecular theory and a modified Leslie-Ericksen continuum theory were used to predict the experimental results. While the Doi theory agreed with both steady shear and steady extensional data, it failed to predict the transient stress growth data. On the other hand, the modified Leslie-Ericksen theory gave a better qualitative prediction of the transient curve, although it predicted that both steady shear viscosity and steady extensional viscosity were constants. The steady state data agrees with the results obtained by Metzner et al., who used a fiber-spinning technique

Effect of salt on the phase diagrams of two binary lyotropic liquid crystalline solutions

Abstract The effect of adding salts NH4OH and CsOH to aqueous solutions of NH4PFO and CsPFO, respectively, was studied for concentrations in the range 0 to 2 wt %. In both systems, the isotropic to nematic and nematic to lamellar phase transition temperatures were elevated. There was an insignificant effect on the width of the nematic range in the NH4PFO system, while the nematic phase was widened by as much as ∼3°C in the case of CsPFO. High-resolution X-ray scattering measurements were performed to determine the micellar size and its dependence on temperature for 52 wt % NH4PFO solution in water.